The longitudinal side piece of the frame of a chain cconveyor consists of two right-angled C profiled parts (12, 14) arranged one above the other at a distance apart and fastened by means of connecting plates (56, 58), clamps (70) seated in the profiled parts (12, 14) and clamping bolts (74) engaging in the connecting plates as well as by means of holding bolts (76) which pass through the profiled parts and engage in the connecting plates (56, 58). The inner space of the lower profiled section (12) provides a supporting surface for the return strand of a conveyor chain, and the upper side of the upper profiled part (14) provides a supporting surface for the driving strand of the conveyor chain. Feet and transverse braces of this type can be mounted at any point on this longitudinal frame side piece. No mechanical machining of the profiled sections is necessary at the junctions.